Electromagnetic balancing forces are well known in the construction of balancing scales. Here the force effect of a conductor, through which an electric current passes, and which is disposed in the magnetic field of a magnet, is used to balance a load, the magnet being as a rule a permanent magnet. As an increasing accuracy is desired, however, the use of permanent magnets poses problems. One of the main problems is the fact that the magnetic flux of a permanent magnet, in addition to being dependent upon other influences, is also temperature-dependent.
Magnetic or magnetizable material for permanent magnets available today, have a reversible temperature coefficient of residual magnetism of the order of -0.2% per degree C. The magnetic flux of a permanent magnet, and consequently the magnetic induction present in an air gap of a magnetic system, of which the permanent magnet is part, and which serves as the balancing system of the scale, thus are reduced in magnitude by two parts in 10,000,/degree C. of temperature increase. Consequently, the generated balancing or measuring force, and hence the indication of the scale is therefore erroneous, and provides an erroneous reading.
For example, a scale having 10,000 digits would indicate, when fully loaded, an error, and consequently, an error in the indication of the scale of two digits per degree of temperature increase in the event of any temperature fluctuation. But, as the electric circuit of a scale, on one hand, and the balancing coil on the other hand, as a result of a current passing therethrough, generates heat, a temperature gradient or field surrounding the magnetic system comes into existence. This results in a superposition of the generally homogeneous temperature region of the surrounding temperature, and a relatively strong non-homogeneous temperature field caused by the heat generated by the system itself. Both the temperature fields or regions superimposed on one another can be subjected to fluctuation in dependence of time. Thus, the surrounding or ambient temperature may fluctuate as a result of cooling or heating, as well as the heat generated by the balancing system itself, as a result of any changes in the load, supply fluctuations and the like. In particular, the non-homogeneous temperature field or region, due to heat generated by the system itself, is built up following activation of the balancing scale itself.
All known temperature compensation systems have the disadvantage, however, that they operate with acceptable accuracy only in the presence of homogeneous temperature fields or regions. If the temperature field or region is changed as a function of time, or due to any homogeneous local distribution of the temperature, large deviations arise, as the magnetic materials causing these errors have different temperatures than the compensating materials and/or the temperature sensing means used.